Immunoglobulin Structure

Immunology

1. Immunology ( Immunoglobulin Structure) By Ahmed Riyadh Abdul Rahman Al-Noor University College 1

2. 2 Immunoglobulin Structure   An antibody or immunoglobulin ( Ig ) is is a large, Y-shaped a glycoprotein produced mainly by plasma cells . There are five classes of human antibodies; all share a basic structure that varies in order to accomplish specific biological functions .

3. Immunoglobulin (Antibody) Structure Enzymatic fragmentation and chemical reduction with Pepsin and papain show that All immunoglobulin molecules have a basic structure composed of four polypeptide chains : 1-two identical heavy chains (H) and 2-two identical light chains (L) . Each light-chain polypeptide usually consists of about 200-220 amino acids and has a mass of approximately 25,000 Da. Each heavy chain consists of about 440-450 amino acids and has a mass of about 50,000 to 70,000 Da. 3

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5. The two heavy chains (H) are connected together by disulfide bonds , Also Heavy and light chains are connected to each other by disulfide bonds . The heavy chains are structurally distinct for each immunoglobulin class or subclass.

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7. Both light (L) and heavy (H) chains contain two different regions : 1-The constant (C)regions (CL and CH): have amino acid sequences that do not vary significantly between antibodies of the same class . 2-The variable (V) regions ( VLand VH): have different amino acid sequences, and these regions fold together to form the antigen-binding sites.

8. 8 Heavy Chains The heavy chain also has a variable region (VH) at its amino terminal domain. The other domains of the heavy chains are termed constant (C) domains. The constant domains of the heavy chain form the constant (CH) region. The amino acid sequence of this region determines the classes of heavy chains. In humans, there are five different classes or isotypes of heavy chains Each class of Heavy chain has a characteristic amino acid sequence that distinguishes it from the other four classes but all five classes have Significant percentages of amino acid sequence similarities designated by lowercase Greek letters: Gamma (γ), Alpha (α ,( Mu (μ), Delta (δ), and Epsilon (ε), and usually written as (G, A , M, D, or E).

9. 9 The properties of these heavy chains determine, respectively, the five immunoglobulin ( Ig ) classes: IgG , IgA, IgM , IgD , and IgE . Each immunoglobulin class differs in its general properties, half-life, distribution in the body, and interaction with other components of the host’s defensive systems.

10. 10 In many species, there are more subclasses of some heavy chains that differ from one another by only a few amino acids , for example: Humans have 4 subclasses of the IgG isotype called IgG1, IgG2, IgG3, and IgG4. IgA has two subclasses IgA1 and IgA2.

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